JPH11299231A - Power supply unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain stable output without being affected by a primary unit voltage fluctuations. SOLUTION: This power supply unit is provided with a main power supply part having a drive transformer T1 for controlling switching transistors Q1, Q2 and the switching frequencies of the transistors Q1, Q2, and a converter transformer T2 and an auxiliary power supply part having a switching transistor Q3 and a flyback transformer T3, through which current is flowed intermittently by the transistor Q3. A negative voltage which is proportional to the primary input voltage is extracted by a rectifier diode D8 and a smoothing capacitor C7 which are connected to a secondary winding N2 of a flyback transformer T3. The extracted voltage is detected by a correction circuit 20, and corrections are made so as to change the operating point of an overpower protection circuit 12, based on the detected voltage. Thus stable overpower protection can be attained without moving the operating point with respect to also the fluctuations in the primary input voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply device such as a switching regulator composed of a main power supply unit and an auxiliary power supply unit, and in particular, to obtain a stable output without being affected by a primary-side input voltage fluctuation. Power supply device that can be.

[0002]

2. Description of the Related Art Conventionally, a power supply device having a main power supply unit and an auxiliary power supply unit has been configured, for example, as shown in FIG. FIG. 3 shows a power supply device using a current resonance type switching regulator as a main power supply unit. E1 denotes a DC power supply obtained by rectifying a commercial power supply voltage by, for example, a diode bridge rectifier circuit.

[0003] NPN switching transistors Q1 and Q2 are connected in series between the positive and negative electrodes of the DC power supply E1. The intermediate point between the switching transistors Q1 and Q2 is connected to the negative electrode of the DC power supply E1 via the winding Nb0 of the drive transformer T1, the resonance capacitor Cr, and the primary winding P of the converter transformer T2, and is a half-bridge type current resonance type switching. The circuit is configured.

The switching cycle of the switching transistors Q1 and Q2 is determined by the windings Nb1 and Nb2, capacitors Cb1 and Cb2, and resistor Rb of the orthogonal drive transformer T1.
The switching frequency is determined by a series resonance circuit composed of Rb1 and Rb2. Ro1 and Ro2 are starting resistances,
Co indicates a protection capacitor, and D1 and D2 indicate damper diodes.

On the secondary side of the converter transformer T2, a secondary winding S2 for an output voltage for taking out a DC output and a tertiary winding S3 for a control voltage are wound.
The voltage induced in the power supply is full-wave rectified by the rectifier diodes D3 and D4 and supplied to a predetermined circuit as a voltage VO. The voltage VO detects a current and a voltage on the output side to control and protect the main power supply unit. Is driven to drive a constant voltage control circuit (including an overcurrent control circuit) 11 that performs the control.

The tertiary winding S3 of the converter transformer T2 is arranged so that the degree of magnetic coupling with the primary winding P is higher than that of the secondary winding S2. It functions as a detection winding that outputs a voltage to the secondary side while being insulated from the secondary side. The voltage induced in the tertiary winding S3 is rectified by the diode D5, smoothed by the smoothing capacitor C3, and is supplied to the overpower protection circuit (constant power control circuit) 12
Supplied to

T3 is a PWM which constitutes an auxiliary power supply unit.
This is the transformer of the flyback converter. One end of the primary winding N1 of the flyback transformer T3 is connected to the positive electrode of the DC power supply E1, and the other end is connected to the negative electrode of the DC power supply E1 via the switching transistor Q3.

A resistor R5 and a diode D6 are connected in series between both ends of the primary winding N1, and a capacitor C4 is connected to the resistor R5 in parallel. C5 is a smoothing capacitor. Secondary winding N2 of flyback transformer T3
Is rectified by the rectifier diode D7 and smoothed by the smoothing capacitor C6.

The constant voltage control circuit 11 for performing the constant voltage control and the overcurrent control and the overpower protection circuit 12 for performing the overpower control (constant power control) are described in, for example, Japanese Patent Application Laid-Open No. 7-284270.
And the circuit shown in FIG.

FIG. 4 does not show the parts constituting the switching regulator of FIG. CCB surrounded by a dashed line in FIG. 4 is a control circuit that controls the drive transformer T1 to perform overpower control, overcurrent control, and constant voltage control, and a differential circuit as a detection circuit for performing constant voltage control. An amplifier OP1, a differential amplifier OP2 as a detection circuit for performing overcurrent control, and a differential amplifier OP3 as a detection circuit for performing overpower control are provided. The output of each of these differential amplifiers drives the transistor Q4 so that a control current flows through the control winding Nc of the drive transformer T1.

Ea, Eb and Ec are reference voltage sources, resistors R1 and R2 are voltage-dividing resistors for detecting the output voltage VO of the secondary winding S2, and R3 and R4 are output voltages of the tertiary winding S3. V
3 shows a voltage dividing resistor for detecting No. 3. The resistance Rd indicates a detection resistance for detecting the current IO supplied to the load.

In the devices shown in FIGS. 3 and 4, switching transistors Q1 and Q2 are controlled to be turned on / off by a predetermined switching frequency, and a current intermittently transmitted by the transistors is converted to a primary winding P of a converter transformer T2.
And an output voltage is obtained at the secondary winding S2.

At this time, a resonance circuit is formed by the resonance capacitor Cr connected in series with the primary winding P of the converter transformer T2, and a maximum output voltage is obtained when the resonance frequency of the resonance circuit matches the switching frequency. Can be

Therefore, when the voltage generated on the output side of the converter transformer T2 is detected to control the current flowing through the control winding Nc of the drive transformer T1 which controls the switching frequency, that is, the drive winding Tc is controlled by the control winding Nc. Control the magnetic saturation characteristics of
By changing the inductance exhibited by the drive windings Nb1 and Nb2, it is possible to control the output-side power supply voltage to be a constant value by changing the switching frequency.

Further, suppression of overvoltage, overcurrent, and overpower is performed by the constant voltage control circuit 11 and the overpower protection circuit 12 (ie, the circuit of FIG. 4) as follows.
That is, a voltage proportional to the output voltage for overvoltage, a voltage proportional to the output current for overcurrent, and a voltage proportional to the output power of the tertiary winding S3 for overcurrent, respectively. When the voltage exceeds the reference voltage sources Ea, Eb, and Ec of the differential amplifiers OP1, OP2, and OP3, the transistor Q4 is driven, and a current flows through the control winding Nc.

Then, the switching frequency of the transistors Q1 and Q2 changes to a predetermined high frequency, thereby increasing the resonance impedance, reducing the drive current of the switching regulator, and limiting the power supplied from the primary side. Things.

[0017]

In the circuits shown in FIGS. 3 and 4, the tertiary winding S3 of the converter transformer T2 is used.
Output voltage (V3) from the secondary side output power (P2 = VO
× IO), and the relationship is as shown in FIG. 5. In order to prevent the output voltage V3 from exceeding a certain value, a current is supplied to the control winding Nc and supplied from the primary side as described above. The constant power control is performed by limiting the power.

However, the output voltage V3 is the primary side input voltage (E
In accordance with the fluctuation of 1), it changes like the characteristic lines a, b, and c in FIG. For this reason, the operating point of the overpower protection circuit fluctuates depending on the primary input voltage, which causes a malfunction of the overpower protection circuit due to the fluctuation of the primary input voltage, and causes a power failure or the like. Failure occurs.

In order to solve the above-mentioned problem, in a conventional circuit, a commercial transformer is used as an auxiliary power source, and a voltage proportional to the primary-side input voltage is taken out on the secondary side. Although input voltage correction has been applied, a similar correction circuit has not been realized when the auxiliary power supply is constituted by a switching power supply.

The present invention has been made in view of the above points, and an object of the present invention is to provide a power supply device in which an auxiliary power supply is constituted by a switching power supply, and to provide stable power without being affected by a primary-side input voltage fluctuation. Is to get it.

[0021]

(1) The present invention relates to a switching element and a control means for controlling a switching frequency of the switching element, a main power supply having a converter transformer, a switching element and the switching element. An auxiliary power supply unit having a transformer through which an intermittent current flows, wherein a voltage proportional to a primary-side input voltage is taken out to a secondary side of the auxiliary power supply unit, and the control means is controlled by the voltage. And a correction means for correcting the primary-side input voltage fluctuation.

The control means is provided on the secondary side of the converter transformer of the main power supply unit, and has a degree of magnetic coupling between the primary winding and the output voltage secondary winding for extracting DC output. A tertiary winding for a control voltage arranged densely, a drive transformer for supplying a drive signal to a switching element of the main power supply unit, and a control winding for changing reactance of the drive transformer. And providing overcurrent control to the control winding by supplying a current corresponding to a fluctuation component of the DC voltage output from at least the tertiary winding, and performing secondary power winding of the converter transformer. A current corresponding to an overcurrent component flowing through the control transformer is supplied to a control winding of the drive transformer to perform overcurrent control, and is output from a secondary winding of the converter transformer. A current corresponding to the fluctuation component of the flow voltage is supplied to the control winding of the drive transformer is characterized by performing the constant voltage control.

Further, the correction means is provided on a secondary winding of a transformer of the auxiliary power supply, and obtains a voltage proportional to a primary input voltage at a timing when a switching element of the auxiliary power supply is turned on. It is characterized by having an acquisition circuit.

(2) The correction means includes a control means when the primary input voltage fluctuates, for example, when the primary input voltage is low.
For example, the operating point of the overpower control unit is increased, and correction is made so that the operating point is lowered when the primary-side input voltage is high. As a result, stable overpower protection can be performed without moving the operating point even when the primary-side input voltage fluctuates.

[0025]

Embodiments of the present invention will be described below with reference to the drawings. In FIG. 1, the same parts as those in FIG. 3 are denoted by the same reference numerals. In the present embodiment, a voltage proportional to the primary-side input voltage of the power supply device is taken out by the circuit shown in FIG. 1, and the primary-side input voltage fluctuation of the overpower protection circuit 12 is corrected by the correction circuit 20. .

That is, the cathode of the rectifier diode D8 is connected to the anode side of the rectifier diode D7 which is one end of the secondary winding N2 of the flyback transformer T3 of the auxiliary power supply unit, and the anode of the diode D8 and the secondary winding are connected. N2
, A smoothing capacitor C7 is connected between the other ends of the two, and a common connection point of the diode D8 and the smoothing capacitor C7 is connected to the correction circuit 20.

Here, the voltage between the primary windings of the flyback transformer T3 is V1, and the number of turns of the primary and secondary windings is N.
If the switching transistor Q3 is on, a voltage of V2 = (N2 / N1) V1 is generated between the secondary windings.

In the flyback converter, the rectifying diode D7 and the smoothing capacitor C6 are connected so that the output of the secondary side is taken out at the timing when the switching transistor Q3 is turned off. An output can be taken out when the switching transistor Q3 is on. This is smoothed and the voltage of V2 is subjected to peak rectification, so that 1
A negative voltage proportional to the input voltage on the secondary side can be extracted.

The negative voltage taken out in this way is detected by the correction circuit 20, and according to the detected voltage, the overpower protection circuit 1
Correction for changing the operating point 2 is performed. The correction circuit 20
The overpower protection circuit to which the correction according to
It is configured as shown in FIG.

That is, the base of an NPN transistor Q4 connected between the control winding Nc of the drive transformer T1 and the ground, and the cathode of a diode D5 for rectifying the voltage of the tertiary winding of the converter transformer T2. A resistor R6 and a PNP transistor Q5 are connected in series. A resistor R7 is connected between the base and the emitter of the transistor Q5. The polarity of the polarity shown is between the base of the transistor Q5 and the anode of a diode D8 for extracting a negative voltage proportional to the primary-side input voltage. Zener diode Z _D is connected. FIG. 2B shows only the main part of the circuit of FIG.

In FIG. 2B, when the anode voltage of the diode D8 (ie, the negative voltage -V2 proportional to the primary input voltage) is high, the Zener diode Z _D
, The transistor Q5 is driven, and a base current flows from the tertiary winding S3 to the base of the transistor Q4. As a result, the transistor Q4 is driven, a current flows from the tertiary winding S3 to the control winding Nc, and the operating point of the overpower protection circuit is lowered.

Further (negative voltage -V2 that is proportional to That is the primary input voltage) anode voltage of the diode D8 is low, since that does not exceed the threshold of the Zener diode Z _D, the reverse operation and As a result, the operating point of the overpower protection circuit becomes higher.

FIG. 2 (a) shows an example of a conventional overpower protection circuit which does not perform correction by the primary side input voltage. Figure 2 (a) shows only the main part of the circuit of FIG. 1, the Zener diode Z _D between the ground and the control winding Nc of the drive transformer T1 is configured by connecting. This figure 2
According to (a) and (b), there is provided a power supply device capable of performing stable overpower protection without moving an operating point with respect to a change in a primary-side input voltage by adding only six parts as compared with the related art. It can be seen that it can be configured.

In this embodiment, the overpower protection circuit has been described as an example of a circuit for performing correction. However, the present invention is not limited to this, and correction may be applied to other control circuits such as an overcurrent protection circuit. It is possible to add Further, in the present embodiment, an example in which the diode D8 is connected in reverse polarity to the diode D7 as a circuit for extracting a voltage proportional to the primary-side input voltage to the secondary side has been described, but the present invention is not limited to this. The same effect as described above can be obtained by winding a detection winding separately from the secondary winding of the flyback transformer T3.

[0035]

As described above, according to the present invention, it has conventionally been difficult to realize the auxiliary power supply when the auxiliary power supply is a switching power supply.
The correction by the primary side input voltage of the control circuit such as the overpower protection circuit on the secondary side can be realized by a simple circuit. For this reason, it is possible to prevent danger such as ignition or smoking due to malfunction of the overpower protection circuit or the like, and it is possible to improve the safety of the device with a small number of parts.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a power supply device according to an embodiment of the present invention.

FIGS. 2A and 2B show an overpower protection circuit, in which FIG. 2A is a circuit diagram without correction by a primary-side input voltage, and FIG. 2B is a circuit diagram with correction by a primary-side input voltage to which the present invention is applied;

FIG. 3 is a circuit diagram of a conventional power supply device.

FIG. 4 is a main part circuit diagram of a conventional power supply device.

FIG. 5 is a characteristic diagram showing control characteristics of the overpower protection circuit.

FIG. 6 is a characteristic diagram showing a change in control characteristics of the overpower protection circuit due to a primary-side input voltage.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 ... Constant voltage control circuit 12 ... Over power protection circuit 20 ... Correction circuit E1 ... DC power supply T1 ... Drive transformer T2 ... Converter transformer T3 ... Flyback transformer Q1-Q3 ... Switching transistor Q4, Q5 ... Transistor D7, D8 ... Rectifier diode C6, C7: smoothing capacitor

Claims (8)

[Claims] 1. A main power supply having a switching element and a control means for controlling a switching frequency of the switching element, a converter power supply, and an auxiliary having a switching element and a transformer through which a current intermittently flows by the switching element. A voltage proportional to a primary-side input voltage is taken out to a secondary side of the auxiliary power supply, and the primary-side input voltage fluctuation of the control unit is corrected by the voltage. A power supply device provided with correction means. 2. The control means is provided on a secondary side of a converter transformer of the main power supply unit, and has a degree of magnetic coupling with a primary winding rather than a secondary winding for an output voltage for extracting a DC output. , A control voltage tertiary winding, a drive transformer for supplying a drive signal to the switching element of the main power supply unit, and a control winding for changing the reactance of the drive transformer. The power supply according to claim 1, further comprising: supplying a current corresponding to a fluctuation component of a DC voltage output from at least the tertiary winding to the control winding to perform overpower control. apparatus. 3. The overcurrent control according to claim 2, wherein the control unit supplies a current corresponding to an overcurrent component flowing through a secondary winding of the converter transformer to a control winding of the drive transformer. Item 3. The power supply device according to item 2. 4. The control means according to claim 1, wherein a constant voltage control is performed by supplying a current corresponding to a fluctuation component of a DC voltage output from a secondary winding of said converter transformer to a control winding of said drive transformer. The power supply device according to claim 2, characterized in that: 5. The correction means is provided on a secondary winding of a transformer of the auxiliary power supply, and obtains a voltage proportional to a primary input voltage at a timing when a switching element of the auxiliary power supply is turned on. The power supply device according to claim 1, further comprising a voltage acquisition circuit. 6. The correction means is provided on a secondary winding of a transformer of the auxiliary power supply, and obtains a voltage proportional to a primary input voltage at a timing when a switching element of the auxiliary power supply is turned on. The power supply device according to claim 2, further comprising a voltage acquisition circuit. 7. The auxiliary power supply unit is provided on a secondary winding of a transformer of the auxiliary power supply unit, and obtains a voltage proportional to a primary input voltage at a timing when a switching element of the auxiliary power supply unit is turned on. The power supply device according to claim 3, further comprising a voltage acquisition circuit. 8. The correction means is provided on a secondary winding of a transformer of the auxiliary power supply, and obtains a voltage proportional to a primary input voltage at a timing when a switching element of the auxiliary power supply is turned on. The power supply device according to claim 4, further comprising a voltage acquisition circuit.